The first good thing that worked for me was learning a proper, gopnik style deep squat. Start with finding your comfortable depth, and hold it down for a 30s…1 min, few reps with a couple min break in between. Put your elbows on the inside of knees and gently push them outward, placing palms in a prayer gesture. Don’t forget deep, diaphragmal breathing. Try to hold lumbar spine in a neutral position, don’t overextend or slouch into pseudo depth. Keep feet flat, try to make sure there isn’t a single spot holding most of the weight (like pushing forward and placing weight on the toes) Eventually as your body adapts, start adding more motion: deep squat and gently roll your ankles. Hold your toes and raise hips until your knees are in full extension, then slowly go back. Try to do Cossack squats. Stretch and gently work on hip abductors and flexors.

Since it’s office work, your neck and shoulders are probably angled forward a bit. Use towel exercises and stretch shoulders, discover mobility range that’s hidden from you.

Most importantly, be honest about your ability. Don’t push it, breathe deep, be gentle and try to relax instead of fighting the pressure.

There are some YouTube channels giving simple but effective exercise advice, like Squat University and Workouts by David. They give decent overview of physiology and related dynamic exercises.